I'm a ikelite owner and been trying to find out an exact answer... Obviously ikelite will tell me to upgrade my housing to accomodate the new Sony a7ii but based of looking at photos and the dimensions the new a7iii is only slightly different in size and considering theirs ample room in the housing regardless of the model it shouldn't be an issue.

The majority of the buttons should in theory match up with some buttons length or throws needing adjusting...

But better yet does anyone here own a a7iii and an older a7ii ikelite housing or had the chance to try it and see what the major change is?

I just feel crazy upgrading my camera to a mark 3 and also buying a new housing because 2 buttons don't function!

So was able to get an a7iii to try in my housing, luckily someone on this small island im living on brought an a7iii and was nice enough to let me man handle it to see if it would work!

The shutter button can be pressed and works correctly, the front aperture wont slide or change and the bottom plate would need to be modified to fit...

If you where really stuck and where willing to modify the base plate and make some button throw adjustments and possibly modify them it could be done, but check for your self I don't want anyone buying an a7iii to try fit it in their a7ii housing I'm opting for buying the A7Rii instead as im sure it fits trouble free.

You would probably be better off going with the a7rii because it will fit and function 100% without issue, the housing has a baseplate just for it. I feel like trying to rig up the housing to work for an mk3 is just asking for headache and probably more trouble than it's worth.